Improved mechanical and moisture resistance property of in situ polymerized transparent PMMA/Cellulose composites

This article evaluates the role of cellulosic fillers in a synthetic polymer matrix like polymethylmethacrylate (PMMA) when incorporated by in situ suspension polymerization technique. Cellulose micro/nanofibers (CNF) were extracted from jute fibers and chemically modified with maleic anhydride (MACNF) to increase their interfacial compatibility with PMMA by participation of the MA moiety in the free radical polymerization with MMA. The effect of incorporating MACNF on the physical and mechanical properties of the PMMA matrix was investigated. Optical transparency was retained in the in situ prepared PMMA/cellulose composites (IPMC) similar to that of unreinforced PMMA. Another set of PMMA/cellulose composites was prepared by dispersing MACNF in PMMA matrix by ex situ solution dispersion method (EPMC). The modification of CNF with MA significantly improved the filler/matrix interfacial compatibility and in situ polymerization technique further enhanced the properties of the composites. The high moisture absorption tendency, which is a major drawback of the cellulose filled composites, remarkably reduced in IPMC. POLYM. COMPOS., 36:1748–1758, 2015. © 2014 Society of Plastics Engineers     

Characterization of soda hardwood lignin and the formation of lignin fibers by melt spinning

Lignin fibers were developed from a commercial available soda hardwood lignin (SHL) with a melt‐spinning approach. SHL showed spinnability to form the fine fibers when poly(ethylene oxide) was used as a plasticizer with lignin. The thermal properties of lignin provided valuable information to assist the processing steps of the lignin fiber formation. The guaiacyl/syringyl ratio in SHL was determined by ³¹P‐NMR because it had great influence on the thermal mobility of lignin. A suitable temperature profile for the melt spinning was predicted through rheological studies of lignin. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Spectroscopic studies and evaluation of thermorheological properties of softwood and hardwood lignin

Fourier transform infrared spectroscopy ( FTIR) was used to determine characteristic absorption peaks of softwood kraft lignin and soda hardwood lignin. Remarkable spectral differences were noticed between the different lignins due to their various chemical structures. Proton nuclear magnetic resonance spectrometry (¹H NMR) was employed to analyze the structure of lignin. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry ( MALDI‐TOF) provided important data regarding the molecular weight distribution of lignin. Thermal stability of softwood lignin was found to be remarkably higher than that of hardwood lignin. Softening temperature and glass transition temperature of lignin were measured by differential scanning calorimetry (DSC) which was useful in selecting an optimal temperature profile during extrusion process. Rheological studies provided valuable information about the viscosity of lignins. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of water absorption,freezing and thawing,and photo‐aging on flexural properties of extruded HDPE/rice husk composites

Durability of lingo‐cellulosic fiber composites under environmental conditions such as moisture, freezing and thawing, and UV exposure needs to be determined prior to the use of these composite materials in outdoor applications. Dimensional stability and changes in the flexural strength and stiffness of extruded rice husk filled high‐density polyethylene composites with and without processing additives such as compatibilizers and processing aid were examined after exposing the composites to water, conditions of freeze–thaw cycles, and UV light. Water absorption results indicated a decrease in the rate of penetration of water in the composites in the presence of compatibilizers. The reduction in strength and stiffness after water absorption was lower for composites with compatibilizers than for the composites without any additives. Freezing and thawing experiments also showed the dimensional changes and degradation of strength and stiffness were less in composites with compatibilizers. Presence of processing aid in the composite showed a similar or enhanced water absorption and loss of mechanical properties, compared with those of the composite without processing additives. Although the composites showed a discoloration of the surface after the UV exposure time (745 h) studied, it was found that within this period of UV exposure the flexural strength and stiffness of the composites did not show significant change. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3619–3625, 2006     

Efficient fault-tolerant collision-free data aggregation scheduling for wireless sensor networks

This paper investigates the design of fault-tolerant TDMA-based data aggregation scheduling (DAS) protocols for wireless sensor networks (WSNs). DAS is a fundamental pattern of communication in wireless sensor networks where sensor nodes aggregate and relay data to a sink node. However, any such DAS protocol needs to be cognisant of the fact that crash failures can occur. We make the following contributions: (i) we identify a necessary condition to solve the DAS problem, (ii) we introduce a strong and weak version of the DAS problem, (iii) we show several impossibility results due to the crash failures, (iv) we develop a modular local algorithm that solves stabilising weak DAS and (v) we show, through simulations and an actual deployment on a small testbed, how specific instantiations of parameters can lead to the algorithm achieving very efficient stabilisation.     

Feedback-feedforward control of structures under seismic excitation

While the base acceleration resulting from a seismic activity on a civil engineering structure is not known a priori, it can be measured in real time. In this paper, it is shown that this extra information can be used for achieving a better control of the structure with little additional effort. The approach taken is to augment the equations of motion for the structural system with an appropriate model of the earthquake excitation based on filtering a Gaussian white noise process. The augmented equations of motion are used to determine a control which utilizes both feedback and feedforward compensation. The feedback loop incorporates measurements of the response of the structure into the control law. The information from both the structure and the earthquake excitation model is utilized in the feedforward control law with an observer designed to estimate the states of the eartquake model based upon the base acceleration measurements. A quadratic performance index is used as a measure of optimality of the control algorithms. Results are given which indicate that the proposed method offers advantages in performance over the control method employing only state feedback and that it is also able to improve upon results of the recently develped instntaneous control algorithms. It is also shown that the nostationarity in the earthquake excitation can often be neglected in practical design of linear systems. Finally, a discussion is given of how the method might be coupled with equivalent linearization techniques and extended for use with nonlinear structures.     

Alumina supported MoO3: an efficient and recyclable catalyst for selective oxidation of tertiary nitrogen compounds to N-oxides using anhydrous TBHP as oxidant under mild reaction conditions

Alumina-supported MoO₃ was found to be an efficient heterogeneous and recyclable catalyst for the oxidation of tertiary nitrogen compounds to N-oxides in excellent yields using anhydrous t-BuOOH as oxidant under mild reaction conditions.     

Ionic liquid promoted an improved synthesis of 3,4-dihydropyrimidinones using [bmim]BF4 immobilized Cu (II) acetylacetonate as recyclable catalytic system

An improved method for the synthesis of 3,4-dihydropyrimidinones by one pot cyclocondensation of aldehyde, β-dicarbonyl compound and urea with significant enhancement in reaction rates using room temperature ionic liquid [bmim] BF₄ immobilized Cu(acac)₂ as recyclable catalytic system is described.     

Dispersion of soybean stock‐based nanofiber in a plastic matrix

The focus of this work is the study of the dispersion mechanism of soybean stock‐based nanofibers in a plastic matrix. The cellulose nanofibers were extracted from soybean stock by chemo‐mechanical treatments. These are bundles of cellulose nanofibers with a diameter ranging between 50 and 100 nm and lengths of thousands of nanometers. These nanofibers were characterized by atomic force microscopy and transmission electron microscopy. X‐ray diffraction studies showed that the soybean stock nanofibers had a relative percentage crystallinity of about 48%. Selective chemical treatments increased the cellulose content of soybean stock nanofibers from 41 to 61%. The matrix polymers used in this project were poly(vinyl alcohol) (PVA) and polyethylene (PE). The mechanical properties of nanofiber‐reinforced PVA film demonstrated a 4‐ to 5‐fold increase in tensile strength, as compared to the untreated fiber‐blend‐PVA film. One of the problems encountered in the use of nanoreinforcements lies in the difficulty in ensuring good dispersion of the filler in the composite material. Improved dispersion level of nanofibers within a thermoplastic was achieved by adding ethylene‐acrylic oligomer emulsion as a dispersant. In the solid phase of nanofiber‐blend‐PE composites, the compression‐molded samples showed that improved mechanical properties were achieved with coated nanofibers. Copyright © 2006 Society of Chemical Industry     

Microcomputers Implementation of Digital Control Strategies for Structural Response Reduction

Abstract: In the past, implementation of active structural control strategies employing PC-based hardware has often been problematic, and there seems to be a need to improve the understanding of the issues associated with implementation of digital control, as well as to reduce the excessive computational times required for I/O processes and calculation of control forces. Recently developed hardware based on dedicated digital signal processing (DSP) chips has offered new possibilities for control algorithm implementation. This paper discusses digital control system concepts and specific practical aspects of digital control implementation, including the use of supervision. Details regarding active structural control using the Texas Instruments TMS32OC30 DSP chip and experimental verification of the hardware performance are given.